The invention relates generally to a method for detecting and removing errors exceeding a specific contrast in digital video signals. This is achieved by using an error detector and a filter, which continuously process pixels (picture elements) associated with pictures in a picture sequence in said digital video signals.
Digital video signals usually consist of a sequence of pictures, whereat the pictures are made up of pixels of interlaced video fields. The characteristics of such digital video signals are determined by how they were originated, processed, transmitted, etc. Below, a picture will be referred to as a film frame if the original source material is film, whereas a picture will be referred to as a video field if the original source is video. Conversely, the word "picture" will in some cases mean a "field".
Dependent upon the origin, the digital video signals may contain various characteristic high contrast, peak white or peak black errors. More specifically this may refer to the presence of areas with large differences in pixel values, where the areas are adjacent within one picture, or where the areas have corresponding coordinates in different pictures.
Film originated errors, when film has been transferred to video, usually belong to two or three consecutive fields and are usually caused by scratches or dust. Such film originated errors differ from video originated errors, which are normally part of only one field, e.g. video transmission errors caused by FM-threshold noise resulting in a typical one-dimensional pattern when the picture sequence is monitored.
Known methods for detecting and removing errors exceeding a specific contrast in digital video signals include linear and non-linear processing within one picture or between pictures in the picture sequence. These methods usually include an error detection part and a filtering part. There are methods wherein the filtering part is controlled by an external triggering device.
A difficulty in known methods is that the detection is incapable of accurately separating image and error information contained in the video signals, thus giving large side-effects in loss of resolution or distortion, as well as inability to adapt the filtering in real-time according to specific shapes of errors which are to be removed.